Sai Kung was buzzing with excitement after a whale was spotted in the waters off Millionaire's Beach on Thursday, but conservationists have urged people not to disturb the giant marine mammal.

Video taken by members of the Hebe Haven Yacht Club showed the massive head of what is believed to be a Bryde's whale above water as it opened and closed its jaws before submerging into the depths.

“We're out all the time in that area on the water. And we've never seen anything remotely like it. It was just magnificent,” Catherine Lumsden, one of the witnesses said.

She said the whale kept its distance from the nearby speedboats but was curious and gentle.

“[It] would come up and then we wait and then [it’d] just come up again a little bit further away or a little bit closer. But then eventually it looked like [it] was going out into deeper water,” Lumsden said.

Taison Chang, the Chairman of the Hong Kong Dolphin Conservation Society, explained that the whale was eating.

"It is a very typical foraging behavior of what we can see in Baleen whales... they usually feed by opening wide their mouths and then try to take in a large amount of water and try to filter out the small animals like fishes or shrimps or krill inside the water," Chang said.

Chang also urged the public not to approach the whale, because that increases the risk of pushing it further inland and it could get stranded as a result.

"But if you are already on the boat and you spot the whale, you can just simply keep distance from the whale. Try to give the animal some space. And that may allow the animal to try to look for its way out to go out to open water again," he said.

According to the Hong Kong Dolphin Conservation Society, Bryde’s whales can be found worldwide in tropical to temperate waters. When fully grown, they can reach lengths of up to 15 metres.

In July of 2012, a whale shark was spotted swimming off Lamma Island.

But in 2021, a dead Bryde's whale was found in waters between the SAR and Shenzhen.